This study is designed to test the hypothesis that involuntary exposure to tobacco smoke increases the risk of lung cancer in non-smoking women. It is a population based case-control study of women who have never used tobacco products and develop lung cancer. Cases are rapidly ascertained in five major metropolitan areas: Atlanta, Houston, Los Angeles, New Orleans and San Francisco-Oakland-San Jose Bay Area. Interview data from cases will be compared to two reference groups: a group of non-smoking women from the same geographic area who have colon cancer and a non-smoking population control group selected by random digit dialing and from H.C.F.A. files. Interviews are conducted in the homes of study subjects or their next-of-kin. Detailed information is obtained on involuntary exposure to tobacco smoke during childhood and adult life. Information is also sought on other lung cancer risk factors (potential confounders) such as occupation and industry of employment, diet, residential factors, specific respiratory carcinogens, family history of cancer and demographic characteristics. Urine specimens and hair samples are collected from study subjects for the analysis of their cotinine (a metabolite of nicotine) content. These analyses are performed to validate the subject's reported status with respect to recent smoking habits. Radon monitors are also placed in the home for 48 hours in order to determine the residential level of radon gas. To ensure standardized histologic classification of lung cancer cased, tissue specimens of lung cancer cases are requested from the appropriate pathology department for loan. These specimens from patients in all five cities are then reviewed by one study pathologist. Logistic regression techniques will be used in the analysis to examine risk of lung cancer by histologic type associated with passive smoking while controlling for confounding variables.